— They speak perfect English. How long have they learnt it?— they were seven years old.A.

问题补充：

— They speak perfect English. How long have they learnt it?

— they were seven years old.

A. Since

B. When

C. After

D. Until

答案：

(答案→)A. Since

B. When

C. After

D. Until

解析：A. Since自从，后接一般过去时，主句用现在完成时 B. When当…时候C. After 当…之后 D. Until直到…;句意：他们说英语说得非常的好。他们学习它多长时间了？自从他们7岁的时候。故选A